U.S. patent number 10,495,877 [Application Number 15/779,056] was granted by the patent office on 2019-12-03 for free-form surface lens and head-up display.
This patent grant is currently assigned to PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.. The grantee listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to Yosuke Asai, Satoshi Kuzuhara, Hiroaki Okayama.
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United States Patent |
10,495,877 |
Kuzuhara , et al. |
December 3, 2019 |
Free-form surface lens and head-up display
Abstract
Head-up display includes display device and projection optical
system. Display device displays an image. Projection optical system
includes refraction lens. Projection optical system projects the
image displayed on display device to an observer. Refraction lens
is disposed while inclined with respect to a reference beam. An
incident surface of refraction lens is a concave surface relative
to a side of display device in an X-axis direction. A curvature in
a Y-axis direction of the incident surface is smaller than a
curvature in the X-axis direction.
Inventors: |
Kuzuhara; Satoshi (Osaka,
JP), Okayama; Hiroaki (Nara, JP), Asai;
Yosuke (Osaka, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
N/A |
JP |
|
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Assignee: |
PANASONIC INTELLECTUAL PROPERTY
MANAGEMENT CO., LTD. (Osaka, JP)
|
Family
ID: |
58796670 |
Appl.
No.: |
15/779,056 |
Filed: |
November 28, 2016 |
PCT
Filed: |
November 28, 2016 |
PCT No.: |
PCT/JP2016/004976 |
371(c)(1),(2),(4) Date: |
May 24, 2018 |
PCT
Pub. No.: |
WO2017/094248 |
PCT
Pub. Date: |
June 08, 2017 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20180356631 A1 |
Dec 13, 2018 |
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Foreign Application Priority Data
|
|
|
|
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Dec 1, 2015 [JP] |
|
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2015-234371 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60K
35/00 (20130101); G02B 3/02 (20130101); B60K
37/02 (20130101); G02B 27/286 (20130101); B60K
37/04 (20130101); G02B 27/0101 (20130101); G02B
2027/012 (20130101); B60K 2370/39 (20190501); B60K
2370/334 (20190501); G02B 5/3025 (20130101); B60K
2370/1529 (20190501); G02B 5/3083 (20130101); B60W
2050/146 (20130101); B60R 2300/205 (20130101) |
Current International
Class: |
G02B
27/01 (20060101); B60K 35/00 (20060101); B60K
37/04 (20060101); G02B 3/02 (20060101); G02B
5/30 (20060101); B60W 50/14 (20120101) |
Field of
Search: |
;345/7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2004-126025 |
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Apr 2004 |
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JP |
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2010-049232 |
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Mar 2010 |
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JP |
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2010-152025 |
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Jul 2010 |
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JP |
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2011-247997 |
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Dec 2011 |
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JP |
|
2013-041182 |
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Feb 2013 |
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JP |
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2013-057897 |
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Mar 2013 |
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JP |
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2014-044244 |
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Mar 2014 |
|
JP |
|
2015-049272 |
|
Mar 2015 |
|
JP |
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2015/141759 |
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Sep 2015 |
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WO |
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Other References
International Search Report of PCT application No.
PCT/JP2016/004976 dated Feb. 7, 2017. cited by applicant.
|
Primary Examiner: Amadiz; Rodney
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
1. A head-up display that causes an observer to visually recognize
a virtual image, the head-up display comprising: a display device
that displays an image; and a projection optical system that
projects the image displayed on the display device onto the
observer, the projection optical system including a refraction
lens, wherein a reference beam that reaches a center of a viewpoint
region of the observer corresponds to a center of the virtual
image, a reference outside beam that reaches the center of the
viewpoint region of the observer corresponds to a vehicle outside
end of the virtual image, an incident surface of the refraction
lens faces the display device on the reference beam, an output
surface of the refraction lens is on an opposite side to the
incident surface on the reference beam, an origin is an
intersection of the reference beam and the incident surface, an
X-axis direction is a straight line including the origin and an
intersection of a tangential plane of the incident surface at the
origin and the reference outside beam, and a Y-axis direction is
perpendicular to the X-axis direction in the tangential plane, the
refraction lens is disposed while inclined with respect to the
reference beam, the incident surface has a concave surface facing
the display device in the X-axis direction, and a curvature of the
incident surface in the Y-axis direction is smaller than a
curvature of the incident surface in the X-axis direction.
2. The head-up display according to claim 1, wherein the output
surface is a convex surface that is convex to a side of the output
surface in the X-axis direction.
3. The head-up display according to claim 1, wherein in the Y-axis
direction, inclination of the output surface to a plane
perpendicular to the reference beam is larger than inclination of
the incident surface to the plane perpendicular to the reference
beam.
4. The head-up display according to claim 1, wherein a curvature of
the output surface in the Y-axis direction is smaller than a
curvature of the output surface in the X-axis direction.
5. The head-up display according to claim 1, wherein the incident
surface of the refraction lens is subjected to anti-reflective
coating.
6. The head-up display according to claim 1, wherein the output
surface of the refraction lens is subjected to anti-reflective
coating.
7. The head-up display according to claim 1, wherein inclination of
the output surface in the Y-axis direction to the reference beam is
larger than inclination of the incident surface in the Y-axis
direction to the reference beam.
8. The head-up display according to claim 1, wherein the projection
optical system projects the virtual image onto a windshield.
9. The head-up display according to claim 1, wherein the projection
optical system includes a reflection member having transparency and
reflectivity.
10. A free-form surface lens used in an imaging optical system that
makes a conjugate relationship between a first image surface and a
second image surface, the free-form surface lens comprising: a
first optical surface; and a second optical surface, wherein a
reference beam that passes through the first optical surface and
the second optical surface corresponds to a center of the second
image surface, and an X-axis direction and a Y-axis direction are
orthogonal to each other in a tangential plane of the first optical
surface at an intersection of the reference beam and the first
optical surface, the first optical surface is a concave surface in
the X-axis direction, and the curvature of the first optical
surface in the Y-axis direction is smaller than the curvature of
the first optical surface in the X-axis direction.
11. The free-form surface lens according to claim 10, wherein in
the Y-axis direction, an angle formed between the first optical
surface and the reference beam is larger than an angle formed
between the second optical surface and the reference beam.
12. The free-form surface lens according to claim 10, wherein the
second optical surface is a convex surface in the X-axis direction,
the curvature of the second optical surface in the X-axis direction
is smaller than the curvature of the first optical surface in the
X-axis direction, and the curvature of the second optical surface
in the Y-axis direction is smaller than the curvature of the second
optical surface in the X-axis direction.
13. The free-form surface lens according to claim 10, wherein a
sectional shape is a wedge shape in a plane passing through an
intersection of the reference beam and the first optical surface
and is perpendicular to the X-axis direction.
14. The free-form surface lens according to claim 10, wherein a
length in the X-axis direction of an image formed by the imaging
optical system when the reference beam passes through the free-form
surface lens is longer than a length in the Y-axis direction.
15. The free-form surface lens according to claim 10, wherein a
length in the X-axis direction of the first optical surface is
longer than a length in the Y-axis direction of the first optical
surface.
16. The free-form surface lens according to claim 10, wherein the
free-form surface lens is a concave lens as a whole.
17. The free-form surface lens according to claim 10, wherein the
free-form surface lens is disposed on an optical path connecting
the first image surface and the second image surface, on the
optical path connecting the first image surface and the second
image surface, the first image surface, the first optical surface,
the second optical surface, and the second image surface are
disposed in this order, and the first image surface is smaller than
the second image surface in an area.
18. The free-form surface lens according to claim 10 disposed in a
head-up display.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a U.S. national stage application of the PCT
International Application No. PCT/JP2016/004976 filed on Nov. 28,
2016, which claims the benefit of foreign priority of Japanese
patent application No. 2015-234371 filed on Dec. 1, 2015, the
contents all of which are incorporated herein by reference.
TECHNICAL FIELD
The present disclosure relates to a head-up display that projects
light on a transparent reflection member to present a virtual
image, and to a free-form surface lens and the like used to project
the light.
BACKGROUND ART
PTL 1 discloses a head-up display device that projects a displayed
image on a windshield. The head-up display device includes a liquid
crystal display, a standard light source, a concave mirror, and a
concave lens. The liquid crystal display generates a basic image to
be a base of a displayed image. The standard light source radiates
light from a rear surface side toward the liquid crystal display.
The concave mirror reflects a light image of the basic image to
project a displayed image on a windshield. The concave lens has a
plano-concave lens shape in which a flat surface is oriented toward
a liquid crystal display side. The concave lens is positioned
between the liquid crystal display and the concave mirror.
PTL 2 discloses a head-up display device that projects a displayed
image on a windshield. The head-up display device includes a liquid
crystal display, a standard light source, a concave mirror, and a
free-form surface lens. The liquid crystal display generates a
basic image to be a base of a displayed image. The standard light
source radiates light from a rear surface side toward the liquid
crystal display. The concave mirror reflects a light image of the
basic image to project a displayed image on the windshield. The
free-form surface lens has a plano-concave lens shape in which a
flat surface is oriented toward a liquid crystal display side. The
free-form surface lens is positioned between the liquid crystal
display and the concave mirror.
CITATION LIST
Patent Literatures
PTL 1: Unexamined Japanese Patent Publication No. 2004-126025
PTL 2: Unexamined Japanese Patent Publication No. 2011-247997
SUMMARY OF THE INVENTION
Technical Problem
The present disclosure provides a head-up display that presents a
high-contrast, little distortion virtual image to effectively
prevent stray light caused by external light.
Solution to Problem
A head-up display of the present disclosure is a head-up display
that causes an observer to visually recognize a virtual image. The
head-up display includes a display device and a projection optical
system. The display device displays an image. The projection
optical system includes a refraction lens. The projection optical
system projects the image displayed on the display device onto the
observer. It is assumed that a reference beam is a beam that
reaches a center in a viewpoint region of the observer and
corresponds to a center of the virtual image. It is assumed that a
reference outside beam is a beam that reaches the center in the
viewpoint region of the observer and corresponds to a vehicle
outside end of the virtual image. An incident surface of the
refraction lens is a surface on a display device side on the
reference beam. An output surface of the refraction lens is a
surface on an opposite side to the incident surface on the
reference beam. It is assumed that an origin is an intersection of
the reference beam and the incident surface. It is assumed that an
X-axis direction is a direction of a straight line including the
origin and an intersection of a tangential plane of the incident
surface at the origin and the reference outside beam. It is assumed
that a Y-axis direction is a direction perpendicular to the X-axis
direction in the tangential plane. At this point, the refraction
lens is disposed while inclined with respect to the reference beam.
The incident surface has a concave surface relative to the display
device side in the X-axis direction. A curvature in the Y-axis
direction of the incident surface is smaller than a curvature in
the X-axis direction of the incident surface.
Advantageous Effect of Invention
The head-up display of the present disclosure is effective in
presenting the high-contrast, little distortion virtual image to
prevent the stray light caused by the external light.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is schematic diagram illustrating a vehicle equipped with a
head-up display according to a first exemplary embodiment.
FIG. 2 is a schematic diagram illustrating a configuration of the
head-up display of the first exemplary embodiment.
FIG. 3 is a schematic diagram illustrating the configuration of the
head-up display of the first exemplary embodiment.
FIG. 4 is a schematic diagram illustrating a configuration of a
projection optical system of the first exemplary embodiment.
FIG. 5 is a schematic diagram illustrating the configuration of the
projection optical system of the first exemplary embodiment.
FIG. 6 is a view illustrating a state in which external light is
incident on the head-up display of the first exemplary
embodiment.
FIG. 7 is a schematic diagram illustrating a configuration of a
head-up display according to a second exemplary embodiment.
FIG. 8 is a view illustrating a state in which the external light
is incident on the head-up display of the second exemplary
embodiment.
FIG. 9 is a schematic diagram illustrating a configuration of a
head-up display according to a third exemplary embodiment.
FIG. 10 is a view illustrating a state in which the external light
is incident on the head-up display of the third exemplary
embodiment.
FIG. 11 is a view illustrating operation of the head-up display of
the third exemplary embodiment.
FIG. 12 is a schematic diagram illustrating a configuration of a
head-up display according to a fourth exemplary embodiment.
FIG. 13 is a view illustrating a state in which the external light
is incident on the head-up display of the fourth exemplary
embodiment.
FIG. 14 is a view illustrating the operation of the head-up display
of the fourth exemplary embodiment.
FIG. 15 is schematic diagram illustrating a vehicle equipped with a
head-up display of a fifth exemplary embodiment.
FIG. 16 is a schematic diagram illustrating the configuration of
the head-up display of the fifth exemplary embodiment.
FIG. 17 is a view illustrating the operation of the head-up display
of the fifth exemplary embodiment.
FIG. 18A is a view illustrating a lens shape of the first to fourth
exemplary embodiments.
FIG. 18B is a view illustrating a lens shape of the first to fourth
exemplary embodiments.
FIG. 18C is a view illustrating a lens shape of the first to fourth
exemplary embodiments.
FIG. 18D is a view illustrating a lens shape of the first to fourth
exemplary embodiments.
FIG. 19A is a view illustrating a lens shape of the fifth exemplary
embodiment.
FIG. 19B is a view illustrating a lens shape of the fifth exemplary
embodiment.
FIG. 19C is a view illustrating a lens shape of the fifth exemplary
embodiment.
FIG. 19D is a view illustrating a lens shape of the fifth exemplary
embodiment.
DESCRIPTION OF EMBODIMENTS
Hereinafter, exemplary embodiments will be described in detail with
reference to the drawings as appropriate. However, the detailed
description more than necessary may be omitted. For example, the
detailed description of already known matters and the overlapping
description of the substantially same configuration may be omitted.
Such omissions are aimed to prevent the following description from
being redundant more than necessary, and to help those skilled in
the art to easily understand the following description.
Note that the attached drawings and the following description are
provided for those skilled in the art to fully understand the
present disclosure, and are not intended to limit the subject
matter as described in the appended claims.
First Exemplary Embodiment
A first exemplary embodiment will be described below with reference
to FIGS. 1 to 6.
[1-1. Configuration]
[1-1-1. Overall Configuration of Head-Up Display]
Specific exemplary embodiments and examples of head-up display 100
of the present disclosure will be described below with reference to
the drawings.
FIG. 1 is a view illustrating a section of vehicle 200 equipped
with head-up display 100 of the present disclosure. As illustrated
in FIG. 1, head-up display 100 is disposed in dashboard 210 below
windshield 220 of vehicle 200. Observer D recognizes an image
projected from head-up display 100 as virtual image I.
FIG. 2 is a schematic diagram illustrating a configuration of
head-up display 100 of the first exemplary embodiment. FIG. 3 is a
schematic diagram illustrating the configuration of head-up display
100 of the first exemplary embodiment.
As illustrated in FIG. 2, head-up display 100 includes display
device 110 and projection optical system 120. Head-up display 100
projects an image displayed by display device 110 onto windshield
220. The projected light is reflected by windshield 220, and guided
to viewpoint region 300 of observer D. Consequently, head-up
display 100 causes observer D to visually recognize virtual image
I.
In the present disclosure, a front refers to a direction in which
the windshield of vehicle 200 exists as seen from observer D. A
rear refers to an opposite direction to the front. A bottom refers
to a direction of a ground on which vehicle 200 runs. A top refers
to an opposite direction to the bottom. An outside refers to a left
side as seen from observer D in the case where vehicle 200 is a
left-hand drive car. At this point, an inside refers to a right
side as seen from the observer. Viewpoint region 300 is a region
where observer D can visually recognize complete virtual image
I.
As illustrated in FIG. 2, it is assumed that reference beam Lc is
an optical path from a center of the image in display device 110 to
a viewpoint of observer D. That is, when seen from observer D,
reference beam Lc corresponds to the optical path from the center
of virtual image I to the viewpoint of observer D. It is assumed
that a reference outside image end is a display position on display
device 110, the display position corresponding to a vehicle outside
end of virtual image I. It is assumed that a reference inside image
end is a display position on display device 110, the display
position corresponding to a vehicle inside end of virtual image I.
It is assumed that reference outside beam Lo is an optical path
from the reference outside image end of display device 110 to the
viewpoint of observer D. That is, reference outside beam Lo is the
optical path of the light corresponding to the vehicle outside end
of virtual image I. Similarly, it is assumed that reference inside
beam Li is an optical path from the reference inside image end of
display device 110 to the viewpoint of observer D. At this point,
it is assumed that the viewpoint of observer D is located in the
center of viewpoint region 300.
Display device 110 displays displayed image 111 under the control
of a controller such as a CPU (not illustrated). For example, a
liquid crystal display with a backlight, an organic light emitting
diode (electroluminescence), a plasma display, and the like can be
used as display device 110. An image may be generated using a
screen that diffuses or reflects the light and a projector or a
scanning laser as display device 110. Various pieces of information
such as road traffic navigation display, a distance to a vehicle
ahead, a remaining battery amount of a vehicle, and a current
vehicle speed can be displayed on display device 110. Display
device 110 can cause observer D to visually recognize good virtual
image I by electronically distorting the image in advance according
to a distortion generated in projection optical system 120 or
windshield 220 and a position of observer D obtained by camera 170.
Display device 110 can also cause observer D to visually recognize
good virtual image I by displaying display pixels of a plurality of
wavelengths while displacing the display pixel in each display
position in advance according to a chromatic aberration generated
in the projection optical system 120.
Projection optical system 120 includes lens 121 having a free-form
surface shape and mirror 122 having a concave reflection surface.
Projection optical system 120 projects the image displayed by
display device 110 onto windshield 220. Specifically, image light
displayed by display device 110 is incident on mirror 122 through
lens 121. Mirror 122 reflects the image light and projects the
reflected image light onto windshield 220.
[1-1-2. Configuration of Projection Optical System]
A configuration of projection optical system 120 will be described
below with reference to FIGS. 2 to 4 and 18A to 18D.
As illustrated in FIG. 3, lens 121 is located on a front side of
vehicle 200 with respect to display device 110. As illustrated in
FIG. 4, lens 121 is disposed while inclined downward with respect
to reference beam Lc.
As illustrated in FIGS. 18A to 18D, lens 121 is a free-form surface
lens in which an X-axis direction and a Y-axis direction differ
from each other in a curvature. A surface (incident surface) facing
110 of lens 121 has a concave shape that is concave to the side of
display device 110 in the X-axis direction. In the incident surface
of lens 121, the curvature in the Y-axis direction is smaller than
the curvature in the X-axis direction. That is, the shape of lens
121 in the Y-axis direction has a concave, convex, or planar shape
in which the curvature in the Y-axis direction is smaller than that
in the X-axis direction. A surface (output surface), on the side of
mirror 122, of lens 121 has a convex shape that is convex to the
side of mirror 122 in the X-axis direction. The output surface of
lens 121 has a concave shape in the Y-axis direction. In the first
exemplary embodiment, by way of example, the incident surface of
lens 121 has a shape so as not to have refractive power in the
Y-axis direction. In the incident surface of lens 121, a concave
surface in which the curvature is smaller than that in the X-axis
direction may be oriented toward the side of display device 110. In
the incident surface of lens 121, a convex surface may be oriented
toward the side of display device 110. Alternatively, the incident
surface of lens 121 may have a shape that is locally concave,
convex, or planar to the side of display device 110. In the first
exemplary embodiment, the concave surface is oriented toward the
side of mirror 122 in the Y-axis direction of the output surface of
lens 121. Alternatively, the convex surface is oriented toward the
side of mirror 122.
When external light such as sunlight is incident on lens 121 from
mirror 122, the external light is reflected by the output surface
or incident surface of lens 121. When the light reflected by lens
121 is incident on mirror 122, possibly the external light is
projected onto windshield 220, and is visually recognized by
observer D. It is undesirable because the external light disturbs a
viewing field of observer D who drives vehicle 200.
In the first exemplary embodiment, as illustrated in FIG. 4, the
incident surface and the output surface of lens 121 are inclined
downward with respect to reference beam Lc. That is, lens 121 is
inclined downward with respect to reference beam Lc. Consequently,
the reflected light is reflected downward by mirror 122 so as not
to be incident on viewpoint region 300. At this point, desirably
inclination of lens 121 with respect to reference beam Lc is an
angle at which the reflected light of the external light is not
incident on mirror 122 when the external light incident along
reference beam Lc is reflected by the incident surface or output
surface of lens 121. More desirably, the inclination of lens 121
with respect to reference beam Lc is an angle at which the
reflected light of the external light is not incident on mirror 122
when the external light incident on lens 121 from mirror 122 is
reflected by the incident surface or output surface of lens 121.
The inclination of lens 121 with respect to reference beam Lc means
that an optical refraction surface of lens 121 is not horizontal to
a plane perpendicular to reference beam Lc.
The output surface of lens 121 is provided while oriented more
downward than the incident surface. That is, the shape, in the
Y-axis direction, of lens 121 has a wedge shape. When a sectional
shape, along the Y-axis direction, of lens 121 is formed into the
wedge shape, an optical path length of the light passing through
the upper part of lens 121 is longer than an optical path length of
the light passing through the lower part of lens 121. That is, the
optical path length until video light output from display device
110 reaches mirror 122 can be changed according to a position, in
the Y-axis direction, of the light. Consequently, eccentric field
curvature generated in mirror 122 can successfully be
corrected.
As illustrated in FIG. 5, it is assumed that origin O is an
intersection of reference beam Lc and the incident surface of lens
121. It is assumed that tangential plane P is a tangential plane of
the incident surface of lens 121 at origin O. It is assumed that an
X-axis is a straight line including origin O and an intersection of
reference outside beam Lo and tangential plane P. It is assumed
that a Y-axis is a straight line perpendicular to the X-axis on
tangential plane P. In FIG. 5, an inside and outside direction of
the vehicle is matched with the X-axis direction. However, the
present disclosure is not limited thereto.
Mirror 122 is located on the front side of vehicle 200 with respect
to lens 121. Mirror 122 reflects the beam output from lens 121
toward windshield 220. A reflection surface of mirror 122 is
eccentrically disposed. The reflection surface of mirror 122 has a
concave shape. That is, mirror 122 projects the light incident from
lens 121 onto windshield 220 while enlarging the light.
Consequently, the image displayed on display device 110 can be
enlarged and visually recognized as virtual image I by observer D.
Mirror 122 has a free-form surface shape. This is because
distortion of the virtual image due to the reflection is corrected.
This enables observer D to see good virtual image I in whole
viewpoint region 300.
At this point, the incident surface of lens 121 is subjected to
anti-reflective coating by a multi-layer structure of a thin film.
This enables reflectance to be reduced in the incident surface of
lens 121.
At this point, the output surface of lens 121 is subjected to the
anti-reflective coating by the multi-layer structure of the thin
film. This enables reflectance to be reduced in the incident
surface of lens 121. At this point, lens 121 is disposed at a
higher position relative to a lower end of the reflection surface
of mirror 122. This enables head-up display 100 to be thinned in a
top-bottom direction of vehicle 200.
For example, a fine periodical structure such as a sub wavelength
structure (SWS) may be used as the anti-reflective coating.
[1-2. Effects and Others]
Head-up display 100 (an example of the head-up display) of the
first exemplary embodiment is a head-up display that causes
observer D to visually recognize virtual image I. Head-up display
100 includes display device 110 (an example of the display device)
and projection optical system 120. Display device 110 displays the
image. Projection optical system 120 includes lens 121 (an example
of the refraction lens), and projects the image displayed on
display device 110 onto observer D. It is assumed that reference
beam Lc is a beam from the center of virtual image I toward the
viewpoint of observer D when the viewpoint of observer D exists in
the center of viewpoint region 300. It is assumed that reference
outside beam Lo is a beam from the vehicle outside end of virtual
image I toward the viewpoint of observer D when the viewpoint of
observer D exists in the center of viewpoint region 300. The
incident surface of lens 121 is an optical surface facing 110 on
reference beam Lc. The output surface of lens 121 is an optical
surface on the opposite side to the incident surface on reference
beam Lc. It is assumed that origin O is the intersection of
reference beam Lc and the incident surface of lens 121. It is
assumed that tangential plane P is the tangential plane of the
incident surface of lens 121 at origin O. It is assumed that the
X-axis direction is a direction of the straight line including
origin O and the intersection of reference outside beam Lo and
tangential plane P. It is assumed that the Y-axis direction is a
direction perpendicular to the X-axis direction in tangential plane
P. Lens 121 is disposed oblique to reference beam Lc. The incident
surface, facing 110, of lens 121 forms a concave surface with
respect to the side of display device 110 in the X-axis direction.
The curvature of the incident surface of lens 121 in the Y-axis
direction is smaller than the curvature of the incident surface in
the X-axis direction.
Lens 121 (an example of the free-form surface lens) of the first
exemplary embodiment is used in an imaging optical system that
makes a conjugate relationship between a first image surface and a
second image surface. The free-form surface lens of the present
disclosure includes a first optical surface and a second optical
surface as the optical surface. The first optical surface
corresponds to the incident surface of lens 121. The second optical
surface corresponds to the output surface of lens 121. The imaging
optical system of head-up display 100 forms a real image (first
image surface) that is the image displayed on display device 110 as
virtual image I (second image surface) visually recognized by
observer D. That is, the imaging optical system of head-up display
100 makes the conjugate relationship between the first image
surface and the second image surface using lens 121. Reference beam
Lc of head-up display 100, namely, the beam corresponding to the
center of the second image surface passes through the first optical
surface and second optical surface of lens 121. At this point, it
is assumed that tangential plane P is the tangential plane of the
first optical surface at the intersection of reference beam Lc and
the first optical surface. The X-axis direction and Y-axis
direction of lens 121 are two directions orthogonal to each other
in tangential plane P, and are similar to those in FIGS. 18A to
19D.
According to the free-form surface lens of the present disclosure,
in the imaging optical system of head-up display 100, a good
optical characteristic can be provided while the reflection of the
external light is prevented.
In lens 121, the curvature in the X-axis direction means the
curvature of the sectional shape in the plane, which includes the
X-axis and is perpendicular to the Y-axis direction. The curvature
in the Y-axis direction means the curvature of the sectional shape
in the plane, which includes the Y-axis and is perpendicular to the
X-axis direction.
Projection optical system 120 of head-up display 100 includes lens
121 and mirror 122 in order from display device 110 on the optical
path.
Head-up display 100 of the first exemplary embodiment projects the
image displayed on display device 110 onto windshield 220, and
causes observer D to visually recognize virtual image I.
Consequently, observer D can visually recognize the image displayed
on display device 110 without obstructing a front viewing field of
observer D.
According to head-up display 100 of the present disclosure, a small
head-up display in which image distortion is successfully corrected
on whole viewpoint region 300 can be constructed. According to the
configuration of the present disclosure, furthermore, a head-up
display that prevents generation of stray light caused by the
external light can be constructed. That is, observer D can visually
recognize good virtual image I even if observer D observes virtual
image I at any position in viewpoint region 300.
Lens 121 of the first exemplary embodiment is disposed while
inclined downward with respect to reference beam Lc. Consequently,
the external light such as the sunlight can be prevented from being
incident on viewpoint region 300 even if the external light is
reflected by the output surface or incident surface of lens 121 as
illustrated in FIG. 6.
The X-axis direction of lens 121 has negative refractive power.
Consequently, a spread, in the X-axis direction, of the beam, which
is output from display device 110 and is incident on lens 121, can
be prevented. This enables head-up display 100 to present virtual
image I having the good contrast characteristic.
The shape of Lens 121 in the X-axis direction is a negative
meniscus shape in which the concave surface is oriented toward
display device 110. Consequently, the angle at which the beam
output from display device 110 is incident on the lens surface of
lens 121 can be brought close to an angle perpendicular to the
incident surface. This enables reduction of an influence of
eccentric distortion.
The output surface of lens 121 has a free-form surface shape.
Specifically, lens 121 is not symmetric in the X-axis direction.
Consequently, in lens 121, asymmetric distortion generated in
windshield 220 can successfully be corrected.
The Y-axis direction of the output surface of lens 121 is inclined
downward compared with the Y-axis direction of the incident surface
of lens 121. That is, based on the plane perpendicular to reference
beam Lc, the inclination in the Y-axis direction of the output
surface of lens 121 is larger than the inclination in the Y-axis
direction of the incident surface of lens 121. In other words, an
angle formed between reference beam Lc and the tangential plane at
the intersection of reference beam Lc and the output surface is
smaller than an angle formed between reference beam Lc and the
tangential plane at the intersection of reference beam Lc and the
incident surface. When the incident surface and the output surface
of lens 121 are inclined, the reflected light of the sunlight can
be prevented from being incident on viewpoint region 300 even if
the sunlight is reflected on the output surface side. Since the
Y-axis direction of the output surface of lens 121 is inclined
downward compared with the Y-axis direction of the incident surface
of lens 121, the optical path length of the light passing through
the upper part of lens 121 is longer than the optical path length
of the light passing through the lower part of lens 121. This
enables the optical path length to be changed according to the
position, in the Y-axis direction, of the light passing through
lens 121. Consequently, the eccentric field curvature generated in
mirror 122 can successfully be corrected.
The incident surface of lens 121 is subjected to the
anti-reflective coating. Consequently, observer D can visually
recognize good virtual image I without decreasing transmittance of
the image displayed on display device 110. Luminance can
sufficiently be decreased even if the external light such as the
sunlight is multiple-reflected between the incident surface and the
output surface of lens 121 to reach viewpoint region 300.
The output surface of lens 121 is subjected to the anti-reflective
coating. Consequently, observer D can visually recognize good
virtual image I without decreasing transmittance of the image
displayed on display device 110. The luminance can sufficiently be
decreased even if the external light such as the sunlight is
multiple-reflected between the incident surface and the output
surface of lens 121 to reach viewpoint region 300.
Generally, the luminance of the light multiple-reflected between
the incident surface and the output surface is lower than the
luminance of the light reflected by the incident surface or the
output surface only once. Even if the luminance of the
multiple-reflected light is degraded, the effect is insufficiently
obtained when the luminance of the light reflected only once is
insufficiently decreased. In the first exemplary embodiment, since
the incident surface and the output surface are inclined to
reference beam Lc, the light reflected by the incident surface or
the output surface only once does not reach mirror 122.
Consequently, the large effect is obtained by preventing the
multiple-reflected light.
In the multiple-reflected light, the reflected light, which is
reflected by the incident surface, reflected by the output surface,
reflected by the incident surface, and reaches mirror 122, will be
described below. At this point, it is assumed that Ri is
reflectance in the incident surface. Similarly, it is assumed that
Ro is reflectance in the output surface. The luminance of the
reflected light is roughly proportional to a value in which a
square of Ri and Ri are multiplied. In particular, the luminance of
the reflected light can efficiently be decreased by the incident
surface being subjected to the anti-reflective coating. The
luminance of the reflected light can also be decreased in roughly
proportional to the decrease of Ro in the case where the output
surface is subjected to the anti-reflective coating. Because the
luminance of the reflected light is proportional to Ri+Ro in the
light reflected only once, the luminance of the reflected light is
not proportional to Ro even if only Ro is decreased. According to
the configuration of the present disclosure, the luminance of the
reflected light can effectively be decreased by the output surface
being subjected to the anti-reflective coating. Similarly,
according to the configuration of the present disclosure, the
luminance of the reflected light can effectively be decreased in
the case where both the incident surface and the output surface are
subjected to the anti-reflective coating.
In projection optical system 120, lens 121 having negative power as
a whole is disposed immediately after display device 110. In lens
121, a surface on which the light of displayed image 111 displayed
on display device 110 is firstly incident is a concave surface.
This enables enhancement of the positive power of mirror 122.
Consequently, head-up display 100 can be reduced in size.
Lens 121 of the first exemplary embodiment is a concave lens as a
whole. That is, lens 121 is an optical element that acts as the
concave lens in both the X-axis direction and the Y-axis direction.
Consequently, lens 121 can be used as the concave lens in the
imaging optical system. Lens 121 is the free-form surface lens.
Consequently, the optical characteristic of the imaging optical
system can successfully be corrected.
The first optical surface (incident surface) of lens 121 of the
first exemplary embodiment is the concave surface in the X-axis
direction. The curvature of the first optical surface in the Y-axis
direction is smaller than the curvature of the first optical
surface in the X-axis direction. In the X-axis direction of lens
121, an incident angle of the light from the first image surface is
increased in a portion far away from the center of the first
optical surface by increasing the curvature of the first optical
surface in the X-axis direction. Consequently, in the X-axis
direction of lens 121, the degradation of the optical
characteristic can be prevented in the portion far away from the
center. In particular, when the length in the X-axis direction of
lens 121 is longer than the length in the Y-axis direction of lens
121, generally the X-axis direction is larger than the Y-axis
direction in the degradation of the optical characteristic in the
portion far away from the center of lens 121. When the length in
the X-axis direction of lens 121 is longer than the length in the
Y-axis direction of lens 121, the curvature of the first optical
surface in the Y-axis direction is smaller than the curvature of
the first optical surface in the X-axis direction, so that the
degradation of the optical characteristic can effectively be
prevented. Note that, the length is not limited to the length in
the outer shape of lens 121. That is, the same holds true for the
case where the length corresponding to the X-axis direction of
virtual image I is longer than the length corresponding to the
Y-axis direction of virtual image I.
The second optical surface (output surface) of lens 121 of the
first exemplary embodiment is the convex surface in the X-axis
direction. Consequently, the shape, in the X-axis direction, of the
first optical surface can be formed into the concave surface having
the large curvature. The curvature of the second optical surface in
the X-axis direction is smaller than the curvature of the first
optical surface in the X-axis direction. Furthermore, the curvature
of the second optical surface in the Y-axis direction is smaller
than the curvature of the second optical surface in the X-axis
direction. Consequently, the optical characteristic of lens 121 can
be set to the concave lens as a whole in the X-axis direction and
the Y-axis direction.
The first optical surface and the second optical surface of lens
121 of the first exemplary embodiment are inclined with respect to
the plane perpendicular to reference beam Lc. Consequently, the
reflected light of the light incident along reference beam Lc is
output toward a direction different from reference beam Lc.
Furthermore, the sectional shape in the plane perpendicular to the
X-axis direction of lens 121 is the wedge shape. That is, the
center (optical center) of the curved shape, in the Y-axis
direction, of lens 121 is located away from the center of lens 121,
for example, outside lens 121. Generally, in the portion away from
the optical center in the concave lens, the optical path length is
lengthened and the optical characteristic becomes uneven in the
plane of lens 121 compared with the portion close to the optical
center. On the other hand, in lens 121 of the first exemplary
embodiment, the optical path length is changed in the Y-axis
direction. Consequently, characteristics of other optical elements
are canceled, the optical characteristic of the imaging optical
system in which lens 121 is used can be corrected as a whole.
An area of the first image surface of the imaging optical system in
which the free-form surface lens of the present disclosure is used
is smaller than an area of the second image surface. That is, in
the imaging optical system, the second image surface enlarges the
first image surface or the first image surface reduces the second
image surface. At this point, the optical surface on the first
image surface side (reduction side) of lens 121 is the first
optical surface. The optical surface on the second image surface
side (enlargement side) of lens 121 is the second optical surface.
Consequently, the optical characteristic of the imaging optical
system can be improved while downsizing of the imaging optical
system is achieved.
Second Exemplary Embodiment
Head-up display 100 according to a second exemplary embodiment
differs from that of the first exemplary embodiment in that head-up
display 100 of the second exemplary embodiment includes
quarter-wave plate 123 and polarization cover 101. Points different
from the first exemplary embodiment will mainly be described below
with reference to FIGS. 7 and 8, and the description about the
similar configuration will be omitted.
[2-1. Configuration]
FIG. 7 is a schematic diagram illustrating an optical path for
describing head-up display 100 of the second exemplary embodiment.
As illustrated in FIG. 7, head-up display 100 includes polarization
cover 101, display device 110, and projection optical system 120.
Projection optical system 120 includes lens 121, mirror 122 having
a concave reflection surface, and quarter-wave plate 123.
Projection optical system 120 projects the image displayed by
display device 110 onto windshield 220. Specifically, image light
displayed on display device 110 is incident on mirror 122 through
lens 121 and quarter-wave plate 123. The image light reflected by
mirror 122 is projected onto windshield 220 through polarization
cover 101. In the second exemplary embodiment, polarization cover
101 has action that absorbs P-polarized light while transmitting
S-polarized light. However, this is not limiting, polarization
cover 101 may have action that absorbs or reflects the S-polarized
light while transmitting the P-polarized light. Alternatively,
polarization cover 101 may reflect the P-polarized light while
transmitting the S-polarized light. Polarization cover 101 has a
curved shape. Because polarization cover 101 has the curved shape,
the external light such as the sunlight is prevented from being
reflected by polarization cover 101 and from reaching viewpoint
region 300.
Lens 121 has a configuration similar to that of the first exemplary
embodiment. Specifically, lens 121 is located on the front side of
vehicle 200 with respect to display device 110, and inclined
downward with respect to reference beam Lc. Similarly to FIGS. 18A
to 18D, lens 121 is the free-form surface lens having different
curvatures in the X-axis direction and the Y-axis direction. A
surface (incident surface) facing 110 of lens 121 has a concave
shape that is concave to the side of display device 110 in the
X-axis direction. The curvature of the incident surface of lens 121
in the Y-axis direction is smaller than curvature in the X-axis
direction. The surface (output surface), on the side of mirror 122,
of lens 121 has the convex shape that is convex to the side of
mirror 122 in the X-axis direction. The output surface of lens 121
has a concave shape in the Y-axis direction. In the second
exemplary embodiment, similarly to the first exemplary embodiment,
the incident surface of lens 121 has a shape so as not to have the
refractive power in the Y-axis direction. In the incident surface
of lens 121, a concave surface in which the curvature is smaller
than that in the X-axis direction may be oriented toward the side
of display device 110. In the incident surface of lens 121, the
convex surface may be oriented toward the side of display device
110. Alternatively, the incident surface of lens 121 may have a
shape that is locally concave, convex, or planar to the side of
display device 110. Similarly to the first exemplary embodiment,
the concave surface is oriented toward the side of mirror 122 of
the output surface of lens 121 in the Y-axis direction.
Alternatively, the convex surface is oriented toward the side of
mirror 122.
Similarly to the first exemplary embodiment, the output surface of
lens 121 is inclined downward with respect to reference beam Lc
compared with the incident surface of lens 121, and the output
surface of lens 121 is formed into the wedge shape in the
top-bottom and front-rear section of the vehicle. Consequently,
even if the external light such as the sunlight is reflected by the
output surface and incident surface of lens 121, the reflected
light of the external light is not incident on viewpoint region
300. When the sectional shape, along the Y-axis direction, of lens
121 is formed into the wedge shape, the upper optical path length
is longer than the lower optical path length, and the eccentric
field curvature generated in mirror 122 can successfully be
corrected.
Quarter-wave plate 123 is a planar polarizer located on the front
side of the vehicle with respect to lens 121. Quarter-wave plate
123 has action that outputs the light output from lens 121 while
rotating the polarization of the light by a quarter of wavelength.
Quarter-wave plate 123 is disposed while inclined downward with
respect to the reference beam. Consequently, the external light can
be prevented from reaching viewpoint region 300 even if the
external light such as the sunlight is reflected by quarter-wave
plate 123.
Mirror 122 is located on the front side of vehicle 200 with respect
to quarter-wave plate 123. The reflection surface of mirror 122 is
eccentrically disposed so as to reflect the beam output from
quarter-wave plate 123 toward windshield 220. The reflection
surface of mirror 122 has a concave shape. Consequently, the image
displayed on display device 110 can be enlarged and visually
recognized as virtual image I by observer D. Mirror 122 has a
free-form surface shape. This enables the distortion caused by the
reflection to be corrected such that good virtual image I is
observed in whole viewpoint region 300.
At this point, lens 121 is disposed at a higher position relative
to a lower end of the reflection surface of mirror 122. This
enables head-up display 100 to be thinned in a top-bottom direction
of vehicle 200.
[2-2. Effects and Others]
Head-up display 100 of the second exemplary embodiment includes
display device 110 that displays the image, projection optical
system 120 that projects the image displayed on display device 110,
and polarization cover 101, and projection optical system 120
includes lens 121, quarter-wave plate 123, and mirror 122 in the
order of the optical path from display device 110.
In addition to the effects of the first exemplary embodiment, in
head-up display 100 of the second exemplary embodiment,
quarter-wave plate 123 is disposed on the front side of the vehicle
with respect to lens 121, and polarization cover 101 is disposed
between mirror 122 and windshield 220. Consequently, the luminance
can sufficiently be decreased even if the external light such as
the sunlight is multiple-reflected by the incident surface or
output surface of lens 121 or the display surface of display device
110 to reach viewpoint region 300. As illustrated in FIG. 8, the
sunlight is incident on mirror 122 through polarization cover 101.
Because polarization cover 101 absorbs the P-polarized light, only
the light having an S-polarized component in the sunlight incident
on polarization cover 101 reaches mirror 122. The S-polarized
component light reaching mirror 122 is reflected by mirror 122, and
is incident on quarter-wave plate 123. When the S-polarized
component light is transmitted through quarter-wave plate 123, the
S-polarized light is converted into circularly-polarized light. The
light transmitted through quarter-wave plate 123 is
multiple-reflected by the incident surface or output surface of
lens 121 or the display surface of display device 110, and is
incident on quarter-wave plate 123 again. The circularly-polarized
light incident on quarter-wave plate 123 is transmitted through
quarter-wave plate 123, and converted into the P-polarized light.
That is, when the external light is reflected by lens 121 or
display device 110 and is incident on mirror 122 again, the
reflected light becomes the P-polarized light. Even if the
reflected light of the P-polarized light is reflected by mirror 122
and is incident on polarization cover 101, because polarization
cover 101 absorbs the P-polarized light, the reflected light of the
P-polarized light cannot pass through polarization cover 101.
Consequently, the external light reflected by lens 121 or display
device 110 is hardly recognized as the stray light by observer D.
In particular, the external light multiple-reflected by lens 121 or
display device 110 is hardly recognized as the stray light by
observer D.
Third Exemplary Embodiment
Head-up display 100 according to a third exemplary embodiment
differs from that of the second exemplary embodiment in that
head-up display 100 of the third exemplary embodiment includes
quarter-wave plate 124 and half-wave plate 125. Therefore, points
different from the second exemplary embodiment will be mainly
described below with reference to FIGS. 9 to 11, and the
description about the similar configuration will be omitted.
[3-1. Configuration]
FIG. 9 is a schematic diagram illustrating an optical path for
describing head-up display 100 of the third exemplary embodiment.
As illustrated in FIG. 9, head-up display 100 includes polarization
cover 101, display device 110, and projection optical system 120.
Projection optical system 120 includes lens 121, mirror 122 having
the concave reflection surface, quarter-wave plate 123,
quarter-wave plate 124, and half-wave plate 125.
Projection optical system 120 projects the image displayed by
display device 110 onto windshield 220. Specifically, the image
light displayed on display device 110 is incident on mirror 122
through quarter-wave plate 124, half-wave plate 125, lens 121, and
quarter-wave plate 123. The image light reflected by mirror 122 is
projected onto windshield 220 through polarization cover 101. In
the third exemplary embodiment, polarization cover 101 absorbs the
P-polarized light while transmitting the S-polarized light.
However, polarization cover 101 is not limited to the third
exemplary embodiment. For example, polarization cover 101 may
absorb or reflect the S-polarized light while transmitting the
P-polarized light. Alternatively, polarization cover 101 may
reflect the P-polarized light while transmitting the S-polarized
light.
In the third exemplary embodiment, quarter-wave plate 124 and
half-wave plate 125 are disposed between display device 110 and
lens 121. However, the disposition of quarter-wave plate 124 and
half-wave plate 125 is not limited to the third exemplary
embodiment. For example, quarter-wave plate 124 and half-wave plate
125 may be disposed while the order of quarter-wave plate 124 and
half-wave plate 125 is replaced.
Lens 121 has a configuration similar to that of the first exemplary
embodiment. Specifically, lens 121 is located on the front side of
vehicle 200 with respect to display device 110, and inclined
downward with respect to reference beam Lc. Similarly to FIGS. 18A
to 18D, lens 121 is the free-form surface lens having different
curvatures in the X-axis direction and the Y-axis direction. A
surface (incident surface) facing 110 of lens 121 has a concave
shape that is concave to the side of display device 110 in the
X-axis direction. In the incident surface of lens 121, the
curvature in the Y-axis direction is smaller than the curvature in
the X-axis direction. The surface (output surface), on the side of
mirror 122, of lens 121 has the convex shape that is convex to the
side of mirror 122 in the X-axis direction. The output surface of
lens 121 has the concave shape in the Y-axis direction. In the
third exemplary embodiment, similarly to the first exemplary
embodiment, the incident surface of lens 121 has the shape so as
not to have the refractive power in the Y-axis direction. In the
incident surface of lens 121, a concave surface in which the
curvature is smaller than that in the X-axis direction may be
oriented toward the side of display device 110. In the incident
surface of lens 121, the convex surface may be oriented toward the
side of display device 110. Alternatively, the incident surface of
lens 121 may have a shape that is locally concave, convex, or
planar to the side of display device 110. Similarly to the first
exemplary embodiment, the concave surface is oriented toward the
side of mirror 122 in the Y-axis direction of the output surface of
lens 121. Alternatively, the convex surface is oriented toward the
side of mirror 122.
Similarly to the first exemplary embodiment, the output surface of
lens 121 is inclined downward with respect to reference beam Lc
compared with the incident surface of lens 121, and the output
surface of lens 121 is formed into the wedge shape in the
top-bottom and front-rear section of the vehicle. Consequently,
even if the external light such as the sunlight is reflected by the
output surface and incident surface of lens 121, the reflected
light of the external light is not incident on viewpoint region
300. When the sectional shape, along the Y-axis direction, of lens
121 is formed into the wedge shape, the upper optical path length
is longer than the lower optical path length, and the eccentric
field curvature generated in mirror 122 can successfully be
corrected.
Quarter-wave plate 123 is located on the front side of the vehicle
with respect to lens 121. Quarter-wave plate 123 outputs the light
incident from lens 121 while rotating the polarization of the light
by a quarter of wavelength. Quarter-wave plate 123 is disposed
while inclined downward with respect to reference beam Lc.
Consequently, the external light such as the sunlight can be
prevented from reaching viewpoint region 300 even if the external
light is reflected by quarter-wave plate 123.
Half-wave plate 125 is located on the front side of the vehicle
with respect to display device 110. Half-wave plate 125 outputs the
light incident from display device 110 while rotating the
polarization of the light by a half of wavelength. Half-wave plate
125 is disposed while inclined downward with respect to reference
beam Lc. Consequently, the external light such as the sunlight can
be prevented from reaching viewpoint region 300 even if the
external light is reflected by half-wave plate 125.
Quarter-wave plate 124 is located on the front side of the vehicle
with respect to half-wave plate 125. Quarter-wave plate 124 outputs
the light incident from half-wave plate 125 while rotating the
polarization of the light by a quarter of wavelength. Quarter-wave
plate 124 is disposed while inclined downward with respect to
reference beam Lc. Consequently, the external light such as the
sunlight can be prevented from reaching viewpoint region 300 even
if the external light is reflected by quarter-wave plate 124.
Mirror 122 is located on the front side of vehicle 200 with respect
to quarter-wave plate 123. The reflection surface of mirror 122 is
eccentrically disposed so as to reflect the beam output from
quarter-wave plate 123 toward windshield 220. The reflection
surface of mirror 122 has a concave shape. Consequently, the image
displayed on display device 110 can be enlarged and visually
recognized as virtual image I by observer D. Mirror 122 has a
free-form surface shape. This is because distortion of the virtual
image due to the reflection is corrected. This enables observer D
to see good virtual image I in whole viewpoint region 300.
At this point, lens 121 is disposed at a higher position relative
to a lower end of the reflection surface of mirror 122. This
enables head-up display 100 to be thinned in a top-bottom direction
of vehicle 200.
[3-2. Effects and Others]
Head-up display 100 of the third exemplary embodiment includes
display device 110, projection optical system 120, and polarization
cover 101. Display device 110 displays the image. Projection
optical system 120 projects the image displayed on display device
110. Projection optical system 120 includes half-wave plate 125,
quarter-wave plate 124, lens 121, quarter-wave plate 123, and
mirror 122 in the order of the optical path from display device
110.
In head-up display 100 of the third exemplary embodiment,
quarter-wave plate 123 is provided on the front side of the vehicle
with respect to lens 121 in addition to the configuration of the
first exemplary embodiment. Polarization cover 101 is disposed
between mirror 122 and windshield 220. Consequently, the luminance
can sufficiently be decreased even if the external light such as
the sunlight is multiple-reflected by the incident surface or
output surface of lens 121 or the display surface of display device
110 to reach viewpoint region 300. As illustrated in FIG. 10, only
the S-polarized component light in the sunlight is transmitted
through polarization cover 101 to reach mirror 122. The S-polarized
light incident on mirror 122 is transmitted through quarter-wave
plate 123, and converted into the circularly-polarized light. The
circularly-polarized light transmitted through quarter-wave plate
123 is multiple-reflected by the incident surface or output surface
of lens 121 or the display surface of display device 110, and is
incident on quarter-wave plate 123 again. The reflected light of
the circularly-polarized light incident on quarter-wave plate 123
is converted into the P-polarized light by quarter-wave plate 123,
and is incident on mirror 122. The P-polarized light reflected by
mirror 122 is absorbed by polarization cover 101, and is not
recognized as the stray light by observer D.
In the third exemplary embodiment, furthermore, half-wave plate
125, quarter-wave plate 124, lens 121, quarter-wave plate 123,
mirror 122, and polarization cover 101 are disposed in the order of
the optical path from display device 110. Consequently, even in the
case where the liquid crystal display device is used as display
device 110, observer D can visually recognize good virtual image I
with less degradation of the transmittance. As illustrated in FIG.
11, the display light output as the S-polarized light from display
device 110 is converted into the P-polarized light by half-wave
plate 125. The light output from half-wave plate 125 is converted
into the circularly-polarized light by quarter-wave plate 124. The
light output from quarter-wave plate 124 is transmitted through
lens 121, converted into the S-polarized light by quarter-wave
plate 123, and is incident on mirror 122. The S-polarized light
reflected by mirror 122 is visually recognized as virtual image I
by observer D without being absorbed by polarization cover 101. In
the third exemplary embodiment, the S-polarized light is used as
the display light output from display device 110. However, in the
case where the display light is the P-polarized light, the similar
effect can be obtained by removing half-wave plate 125.
Fourth Exemplary Embodiment
Head-up display 100 according to a fourth exemplary embodiment
differs from that of the third exemplary embodiment in that head-up
display 100 of the fourth exemplary embodiment includes
quarter-wave film 126 while not including quarter-wave plate 123.
Points different from the third exemplary embodiment will mainly be
described below with reference to FIGS. 12 to 14, and the
description about the similar configuration will be omitted.
[4-1. Configuration]
FIG. 12 is a schematic diagram illustrating an optical path for
describing head-up display 100 of the fourth exemplary embodiment.
As illustrated in FIG. 12, head-up display 100 includes
polarization cover 101 to which quarter-wave film 126 is cemented,
display device 110, and projection optical system 120. Projection
optical system 120 includes lens 121, mirror 122 having the concave
reflection surface, quarter-wave plate 124, and half-wave plate
125.
Projection optical system 120 projects the image displayed by
display device 110 onto windshield 220. Specifically, the image
light displayed on display device 110 is incident on mirror 122
through quarter-wave plate 124, half-wave plate 125, and lens 121.
The image light reflected by mirror 122 is projected onto
windshield 220 through quarter-wave film 126 and polarization cover
101. In the fourth exemplary embodiment, polarization cover 101
absorbs the P-polarized light while transmitting the S-polarized
light. However, polarization cover 101 is not limited to the fourth
exemplary embodiment. For example, polarization cover 101 may
absorb or reflect the S-polarized light while transmitting the
P-polarized light. Alternatively, polarization cover 101 may
reflect the P-polarized light while transmitting the S-polarized
light. It is not necessary that quarter-wave film 126 and
polarization cover 101 be cemented together, but quarter-wave film
126 and polarization cover 101 may be provided separately from each
other. Instead of quarter-wave film 126, quarter-wave plate may be
disposed between mirror 122 and polarization cover 101.
In the fourth exemplary embodiment, similarly to the third
exemplary embodiment, quarter-wave plate 124 and half-wave plate
125 are disposed between display device 110 and lens 121. The
disposition of quarter-wave plate 124 and half-wave plate 125 is
not limited to the fourth exemplary embodiment, but quarter-wave
plate 124 and half-wave plate 125 may be disposed while the order
of quarter-wave plate 124 and half-wave plate 125 is replaced.
Lens 121 has a configuration similar to that of the first exemplary
embodiment. Specifically, lens 121 is located on the front side of
vehicle 200 with respect to display device 110, and inclined
downward with respect to reference beam Lc. Similarly to FIGS. 18A
to 18D, lens 121 is the free-form surface lens having different
curvatures in the X-axis direction and the Y-axis direction. A
surface (incident surface) facing 110 of lens 121 has a concave
shape that is concave to the side of display device 110 in the
X-axis direction. In the incident surface of lens 121, the
curvature in the Y-axis direction is smaller than the curvature in
the X-axis direction. The surface (output surface), on the side of
mirror 122, of lens 121 has the convex shape that is convex to the
side of mirror 122 in the X-axis direction. The output surface of
lens 121 has the concave shape in the Y-axis direction. In the
fourth exemplary embodiment, similarly to the first exemplary
embodiment, the incident surface of lens 121 has the shape so as
not to have the refractive power in the Y-axis direction. However,
the incident surface of lens 121 is not limited to the fourth
exemplary embodiment. For example, the incident surface of lens 121
may be a concave surface in which the curvature of the incident
surface of lens 121 in the Y-axis direction is smaller than that of
the X-axis direction of the incident surface. Alternatively, the
incident surface of lens 121 may be convex to the side of display
device 110 in the Y-axis direction. Alternatively, the incident
surface of lens 121 may have a shape that is locally concave,
convex, or planar to the side of display device 110. Similarly to
the first exemplary embodiment, the incident surface of lens 121 is
concave to the side of mirror 122 in the Y-axis direction.
Alternatively, the incident surface of lens 121 may be convex to
the side of mirror 122 in the Y-axis direction.
Similarly to the first exemplary embodiment, the output surface of
lens 121 is inclined downward with respect to reference beam Lc
compared with the incident surface of lens 121, and the output
surface of lens 121 is formed into the wedge shape in the
top-bottom and front-rear section of the vehicle. Consequently,
even if the external light such as the sunlight is reflected by the
output surface and incident surface of lens 121, the reflected
light of the external light is not incident on viewpoint region
300. When the sectional shape, along the Y-axis direction, of lens
121 is formed into the wedge shape, the upper optical path length
is longer than the lower optical path length. Consequently, the
eccentric field curvature generated in mirror 122 can successfully
be corrected.
Quarter-wave film 126 is cemented to the surface side, in the
vehicle bottom direction, of polarization cover 101. Quarter-wave
film 126 outputs the light incident from mirror 122 while rotating
the polarization of the light by a quarter of wavelength. At this
point, because polarization cover 101 has the curved shape,
quarter-wave film 126 also has the curved shape. Consequently, the
external light such as the sunlight is prevented from being
reflected between polarization cover 101 and quarter-wave film 126
and from reaching viewpoint region 300.
Mirror 122 is located on the front side of vehicle 200 with respect
to lens 121. The reflection surface of mirror 122 is eccentrically
disposed so as to reflect the beam output from lens 121 toward
windshield 220. The reflection surface of mirror 122 has a concave
shape. Consequently, the image displayed on display device 110 can
be enlarged and visually recognized as virtual image I by observer
D. Mirror 122 has a free-form surface shape. This is because the
distortion of virtual image due to the reflection is corrected such
that good virtual image I is observed in whole viewpoint region
300.
At this point, lens 121 is disposed at a higher position relative
to a lower end of the reflection surface of mirror 122. This
enables head-up display 100 to be thinned in a top-bottom direction
of vehicle 200.
[4-2. Effects and Others]
Head-up display 100 of the fourth exemplary embodiment includes
display device 110, projection optical system 120, and polarization
cover 101. Display device 110 displays the image. Projection
optical system 120 projects the image displayed on display device
110. Quarter-wave film 126 is cemented to polarization cover 101.
Projection optical system 120 includes half-wave plate 125,
quarter-wave plate 124, lens 121, and mirror 122 in the order of
the optical path from display device 110.
In head-up display 100 of the fourth exemplary embodiment,
quarter-wave film 126 is disposed while cemented below polarization
cover 101 in addition to the effects of the first exemplary
embodiment. Consequently, the luminance can sufficiently be
decreased even if the external light such as the sunlight is
multiple-reflected by the incident surface or output surface of
lens 121 or the display surface of display device 110 to reach
viewpoint region 300. As illustrated in FIG. 13, the sunlight is
incident on quarter-wave film 126 through polarization cover 101.
Consequently, only the S-polarized component light in the sunlight
reaches quarter-wave film 126. The S-polarized light transmitted
through quarter-wave film 126 is converted into the
circularly-polarized light, and reaches mirror 122. The light
reflected by mirror 122 is multiple-reflected between the incident
surface and the output surface of lens 121, and is incident on
mirror 122 again. The circularly-polarized light reflected by
mirror 122 is converted into the P-polarized light by quarter-wave
film 126, and absorbed by polarization cover 101. Thus, the
P-polarized light is not recognized as the stray light by observer
D.
In the fourth exemplary embodiment, half-wave plate 125,
quarter-wave plate 124, lens 121, mirror 122, quarter-wave film
126, and polarization cover 101 are disposed in the order of the
optical path from display device 110. Consequently, even in the
case where the liquid crystal display device is used as display
device 110, observer D can visually recognize good virtual image I
with less degradation of the transmittance. As illustrated in FIG.
14, the display light output as the S-polarized light from display
device 110 is converted into the P-polarized light by half-wave
plate 125. The light output from half-wave plate 125 is converted
into the circularly-polarized light by quarter-wave plate 124. The
light output from quarter-wave plate 124 is incident on mirror 122
through lens 121. Because the circularly-polarized light reflected
by mirror 122 is converted into the S-polarized light by
quarter-wave film 126, the S-polarized light is visually recognized
as virtual image I by observer D without being absorbed by
polarization cover 101. In the fourth exemplary embodiment, the
S-polarized light is used as the display light output from display
device 110. However, the display light is not limited to the
S-polarized light. In the case where the display light is the
P-polarized light, the similar effect can be obtained by removing
half-wave plate 125 from the configuration of the fourth exemplary
embodiment.
In the fourth exemplary embodiment, because quarter-wave film 126
and polarization cover 101 are cemented together, the multiple
reflection of quarter-wave plate 123 and lens 121 needs not to be
considered unlike the third exemplary embodiment.
Fifth Exemplary Embodiment
Head-up display 100 according to a fifth exemplary embodiment
differs from that of the first to fourth exemplary embodiments in
that the virtual image is visually recognized through combiner 127.
Points different from the first to fourth exemplary embodiments
will mainly be described below with reference to FIGS. 15 to 17,
and the description about the similar configuration will be
omitted.
[5-1. Configuration]
FIG. 15 is a view schematically illustrating a section of vehicle
200 equipped with head-up display 100 of the present disclosure. As
illustrated in FIG. 15, head-up display 100 is disposed inside and
outside dashboard 210 below windshield 220 of vehicle 200. Observer
D recognizes the image projected from head-up display 100 as
virtual image I through combiner 127.
FIG. 16 is a schematic diagram illustrating an optical path for
describing head-up display 100 of the fifth exemplary embodiment.
As illustrated in FIG. 16, head-up display 100 includes display
device 110 and projection optical system 120. Projection optical
system 120 includes lens 121 and combiner 127. Combiner 127 is an
optical member having transparency and reflectivity, and includes a
concave reflection surface.
Projection optical system 120 projects the image displayed on
display device 110 onto observer D as virtual image I.
Specifically, the image light displayed on display device 110 is
incident on combiner 127 through lens 121. The image light incident
on combiner 127 is reflected by combiner 127, and projected onto
viewpoint region 300 of observer D. The combiner 127 has the
transparency, so that observer D can check the front of the vehicle
through combiner 127. This enables observer D to visually recognize
virtual image I without disturbing the front viewing field. In the
fifth exemplary embodiment, lens 121 and display device 110 are
disposed below dashboard 210. However, the present disclosure is
not limited to the configuration of the fifth exemplary embodiment.
For example, lens 121 and display device 110 may be disposed such
that a part or whole of head-up display 100 is disposed above
dashboard 210.
Lens 121 is located on the front side of vehicle 200 with respect
to display device 110, and inclined downward with respect to
reference beam Lc.
As illustrated in FIGS. 19A to 19D, lens 121 is the free-form
surface lens in which the X-axis direction and the Y-axis direction
differ from each other in the curvature. A surface (incident
surface) facing 110 of lens 121 has a concave shape that is concave
to the side of display device 110 in the X-axis direction. In the
incident surface of lens 121, the curvature in the Y-axis direction
is smaller than the curvature in the X-axis direction. The surface
(output surface), on the side of combiner 127, of lens 121 has the
convex shape that is convex to the side of combiner 127 in the
X-axis direction. The output surface of lens 121 has a concave
shape in the Y-axis direction. In the fifth exemplary embodiment,
by way of example, the incident surface of lens 121 has the shape
so as not to have refractive power in the Y-axis direction. In the
incident surface of lens 121, a concave surface in which the
curvature is smaller than that in the X-axis direction may be
oriented toward display device 110. In the incident surface of lens
121, the convex surface may be oriented toward display device 110.
Alternatively, the incident surface of lens 121 may have a shape
that is locally concave and convex to the side of display device
110.
In the fifth exemplary embodiment, the output surface of lens 121
has the convex shape having the small curvature in the Y-axis
direction. Alternatively, the output surface of lens 121 may have
the concave shape in the Y-axis direction. As illustrated in FIG.
17, the output surface of lens 121 is inclined downward with
respect to reference beam Lc compared with the incident surface of
lens 121. Consequently, even if the external light such as the
sunlight is reflected by the output surface or incident surface of
lens 121, the reflected light of the external light is not incident
on viewpoint region 300. The sectional shape, along the Y-axis
direction, of lens 121 is the wedge shape. Consequently, the upper
optical path length is longer than the lower optical path length,
so that the eccentric field curvature generated in combiner 127 can
successfully be corrected.
Combiner 127 is located on the front side of vehicle 200 with
respect to lens 121. The reflection surface of combiner 127 is
eccentrically disposed so as to reflect the beam output from lens
121 toward observer D. The reflection surface of combiner 127 has
the concave shape. Consequently, the image displayed on display
device 110 can be enlarged and visually recognized as virtual image
I by observer D. Combiner 127 also has the free-form surface shape.
This enables the correction of the distortion of the virtual image
due to the reflection. Consequently, the correction is performed
such that observer D sees good virtual image I in whole viewpoint
region 300.
[5-2. Effects and Others]
Head-up display 100 of the fifth exemplary embodiment includes
display device 110 and projection optical system 120. Display
device 110 displays the image. Projection optical system 120
projects the image displayed on display device 110. Projection
optical system 120 includes lens 121 and combiner 127 in the order
of the optical path from display device 110.
Head-up display 100 of the fifth exemplary embodiment, the image
displayed on display device 110 is presented as virtual image I to
observer D through combiner 127 in addition to the effects of the
first exemplary embodiment. Consequently, observer D can visually
recognize the image displayed on display device 110 without
obstructing a front viewing field of observer D.
The output surface of lens 121 in the Y-axis direction is formed
into the free-form surface shape having no symmetry. Consequently,
the asymmetric distortion generated in combiner 127 can
successfully be corrected. FIGS. 18A to 18D are views illustrating
the shape of lens 121 of the first to fourth exemplary embodiments.
FIGS. 19A to 19D are views illustrating the shape of lens 121 of
the fifth exemplary embodiment.
However, the lens shapes in FIGS. 18A to 18D and 19A to 19D are not
limited to the exemplary embodiments. The shape of lens 121 in
FIGS. 18A to 18D may be applied to the fifth exemplary embodiment.
The shape of lens 121 in FIGS. 19A to 19D may be applied to the
first to fourth exemplary embodiments.
Other Exemplary Embodiments
The first to fifth exemplary embodiments have been described as
illustration of the technique disclosed in the present application.
However, the technique of the present disclosure is not limited to
the first to fifth exemplary embodiments, but can be applied to
exemplary embodiments in which modifications, replacements,
additions, omissions, and the like are made. Additionally,
components described in the first to fifth exemplary embodiments
can be combined to obtain a new exemplary embodiment.
In the first to fourth exemplary embodiments, by way of example,
lens 121 is used as the refractive optical system provided between
display device 110 and mirror 122. However, the refractive optical
system is not limited to lens 121 that is one lens element. For
example, in the refractive optical system, a plurality of lens
elements may be disposed between display device 110 and mirror 122.
In the case where the plurality of lens elements are disposed,
desirably the surface, facing the display device, of the lens
element on which the light output from the display device is
firstly incident is the concave surface in the X-axis
direction.
In the first to fourth exemplary embodiments, one mirror is
disposed as projection optical system 120. Alternatively, at least
two mirrors may be disposed. The additional mirror may be disposed
on the front side of the vehicle with respect to mirror 122 or in
the inside and outside direction (in FIG. 3, a direction
perpendicular to the paper plane) of the vehicle.
In the first to fourth exemplary embodiments, only lens 121 is
disposed between display device 110 and mirror 122 as the lens
element of projection optical system 120. However, the
configuration of head-up display 100 is not limited to the first to
fourth exemplary embodiments. For example, a lens may additionally
be disposed between mirror 122 and windshield 220.
In the first to fourth exemplary embodiments, mirror 122 of head-up
display 100 has the rotationally asymmetrical shape. However,
mirror 122 is not limited to the mirror having the rotationally
asymmetrical shape. For example, mirror 122 may have what is called
a saddle-type surface shape in which the X-axis direction differs
from the Y-axis direction in a sign of the curvature.
The surface shape of lens 121 of the first to fourth exemplary
embodiments is not limited to the free-form surface shape. For
example, the surface shape of lens 121 may have a toroidal,
anamorphic, or cylindrical shape, or the lens having the toroidal,
anamorphic, or cylindrical shape may eccentrically be disposed with
respect to reference beam Lc.
In the first to fourth exemplary embodiments, the whole incident
surface of lens 121 is not necessarily formed into the concave
surface in the X-axis direction, but may locally have the concave
shape.
In the first to fourth exemplary embodiments, the incident surface
of lens 121 is not necessarily formed into the planar surface in
the Y-axis direction. The incident surface of lens 121 may be
formed into the convex or concave surface, or locally have the
curved surface shape in the Y-axis direction.
In the first to fourth exemplary embodiments, the output surface of
lens 121 is not necessarily formed into the concave surface that is
oriented toward mirror 122 in the Y-axis direction. The output
surface of lens 121 may be formed into the convex or planar
surface, or locally have the curved surface shape in the Y-axis
direction.
In the first to fourth exemplary embodiments, the shape of the
reflection surface of mirror 122 is not limited to the free-form
surface shape. The reflection surface of mirror 122 may have a
spherical, aspherical, toroidal, or anamorphic shape, or the lens
having the spherical, aspherical, toroidal, or anamorphic shape may
eccentrically be disposed with respect to reference beam Lc.
In the second to fourth exemplary embodiments, polarization cover
101 is disposed by way of example. However, the present disclosure
is not limited thereto. For example, polarization cover 101 may be
one in which a cover and an optical member having the polarization
action are disposed separately from each other. Instead of
polarization cover 101, an optical member having polarization
action may be disposed in projection optical system 120. At this
point, desirably the wave plate is not disposed on the rear side of
the optical member having the polarization action in the order of
the optical path from display device 110.
In the third and fourth exemplary embodiments, display device 110,
quarter-wave plate 124, and half-wave plate 125 are disposed
separately from each other by way of example. Alternatively,
display device 110, quarter-wave plate 124, and half-wave plate 125
may be disposed while cemented to one another.
In the third and fourth exemplary embodiments, quarter-wave plate
124 and half-wave plate 125 are disposed separately from each other
by way of example. Alternatively, one wave plate having similar
effects may be disposed as quarter-wave plate 124 and half-wave
plate 125.
In the fourth exemplary embodiment, quarter-wave film 126 is
cemented to polarization cover 101 by way of example.
Alternatively, a curved quarter-wave plate may be disposed. The
curved quarter-wave plate has the effect similar to that of
polarization cover 101. That is, the external light reflected by
the quarter-wave plate can be prevented from reaching viewpoint
region 300 of observer D.
In the fifth exemplary embodiment, one lens element is disposed
between display device 110 and combiner 127 by way of example.
Alternatively, a plurality of lens elements may be disposed. In the
case where the plurality of lens elements exist, desirably a first
incident surface is a concave surface in the X-axis direction. As
used herein, the first incident surface means a surface, facing the
display device, of the lens element on which the light output from
the display device is firstly incident. A reflection member may be
disposed between display device 110 and combiner 127.
In the fifth exemplary embodiment, display device 110 and lens 121
are disposed below dashboard 210. Alternatively, display device 110
and lens 121 may be disposed above dashboard 210.
In the fifth exemplary embodiment, a part of head-up display 100 is
disposed below dashboard 210. Alternatively, a part of head-up
display 100 may be disposed above dashboard 210.
The above exemplary embodiments are illustrations of the technique
of the present disclosure. Therefore, various changes,
replacements, additions, or omissions may be made to the exemplary
embodiments within the scope of claims or their equivalents.
Lens 121 in FIGS. 18A to 19D has a rectangular outer shape
projected onto the XY-plane. However, lens 121 is not limited to
the rectangular outer shape. For example, lens 121 may have an
outer shape in which lens 121 is easily held by head-up display
100.
INDUSTRIAL APPLICABILITY
The present disclosure is applicable to a head-up display that uses
a refractive optical system such as a lens. Specifically, the
present disclosure is applicable to a head-up display for a
vehicle.
REFERENCE MARKS IN THE DRAWINGS
100 head-up display 101 polarization cover (polarization member)
110 display device 111 displayed image 120 projection optical
system 121 lens (refraction lens) 122 mirror 123 quarter-wave plate
(first polarizer) 124 quarter-wave plate (second polarizer) 125
half-wave plate (third polarizer) 126 quarter-wave film (first
polarizer) 127 combiner 170 camera 200 vehicle 210 dashboard 220
windshield (reflection member) 300 viewpoint region D observer I
virtual image
* * * * *